1. Field of the Invention
This invention relates to signal transmitting and reproducing apparatus and, more particularly, to novel and highly-effective signal transmitting/reproducing apparatus of a type suitable for use as a cordless telephone and the like.
2. Description of the Prior Art
The cord of a conventional telephone is connected to a base unit that in turn is attached (rigidly or by another cord) to a post, wall or the like, so that the range of the movement permitted a user of the telephone is limited by the length of the telephone cord, for example several meters. If the telephone cord is longer than a few meters, so as to extend the range of movement permitted the user, the cord is likely to become tangled, to catch on various objects, to pull small objects from tables, to trip or inconvenience other persons in the vicinity, etc. To overcome these problems, so-called cordless telephones are becoming more frequently used in the United States and other countries.
A problem with conventional cordless telephones arises when a single base unit is used in combination with two or more handsets. In such case, a single down channel common to both handsets is used for transmission from the base unit to the handsets and a single up channel common to both handsets is used for transmission from the handsets to the base unit.
Accordingly, when the base unit calls the handsets in response to an incoming call, a telephone buzzer or similar device in each of the handsets generates an audible signal. When users of both handsets answer the call of the base unit, both handsets begin transmitting through the same up channel, which results in radio interference. In the worst case, the base unit becomes unable to receive the signal from either handset and hence no response can be made to the incoming call.
Similarly, if the handsets are used by chance in an attempt to make two outgoing calls at substantially the same time, radio interference and a service interruption result.